1. Field of the Invention
This invention relates to a displacement detector and, more particularly, to an improvement in a displacement detector having a main scale and a grid which relatively move in a state that oppose one another with regular intervals.
2. Description of the Related Art
Such a displacement detector wherein a main scale and a grid move relatively to one another in an opposite state and wherein the relative movement is detected as an electronic signal, is widely utilized in a so-called digital gauge, digital caliper or digital micrometer.
Taking for an example, a digital gauge has a spindle capable of moving along its axis direction in a gauge body, a main scale integrally provided on the spindle, and a grid fixed in the gauge body so as to oppose the main scale, so that the displacement value of the spindle can be detected by converting the relative movement of the main scale and corresponding gird to an electric signal.
It is important to the accuracy of the displacement detector to maintain a regular interval between the main scale and the grid.
The conventional grid has protrusions which contact with a surface of the main scale opposite to the grid, the protrusions being urged by a spring toward the main scale to thereby maintain the regular intervals.
Since to maintain the grid in contact with the main scale can be done by the spring, when the conventional displacement detector is influenced by a sudden impact or vibration while measuring, the grid may be momentary taken off the main scale against the urging force of the spring. At the time, at which the interval between the main scale and the grid becomes wide, electrical malfunctions such as a miss-counting and a miss-display may happen to thereby incorrectly indicate the displacement value.
To solve such problems, separation of the grid from the main scale can be precluded, by using a stronger spring, when the displacement detector is influenced by a sudden impact or vibration while measuring. But, the main scale can not move smoothly, because the protrusions are urged against the main scale too strongly, so that the durability of the detector will be shortened.
An object of the present invention is to solve the mentioned problems and to provide a displacement detector which has such features that the relative movement of the main scale and grid is smooth, the detection of the relative movement value is done accurately when influenced by a sudden impact or vibration while measuring, and the manufacturing cost is reasonable.